1. Field of the Invention
The present invention relates to a disk array system, in particular, to a configuration of a cache memory employed for the disk array system and a control method for the cache memory.
2. Description of Related Art
Conventional disk array systems have a cache memory between disk array adapters coupled to plural disk drives and input/output channels coupled to host computers. Such a cache memory, which can be read/written much faster than the disk drives, stores data to be read/written from/into the disk drive to improve such performance as the data transfer rate, and input/output operations per second. JP-A 233201/1999 and JP-A 290790/2000 disclose such conventional disk array systems.
Some of the conventional disk array systems have physically plural cache memories to improve the reliability of their systems.
Even in this configuration of a system, the plural cache memories is controlled as a single united cache memory. When data is written, the same data need to be written into all of the plural cache memories. In particular, the cache memory disclosed in JP-A 203201/1999, which stores data to be written in a disk drive, is also physically composed of a single non-volatile cache memories.
In those configurations, however, it is difficult to improve the performance of the system including input/output operations per second, since the cache memory is shared among plural input/output channels, thereby accesses of those channels to the cache memory often collide with each other.
Furthermore, because all the input/output channels as well as all the disk adapters must be coupled to the single cache memory, it is difficult to enlarge the disk array system by increasing the number of input/output channels and the number of disk adapters.
Furthermore, because the data must be read from a disk drive to a disk adapter, then passed to the cache memory and then passed to the input/output channel, the path includes many steps and the data input/output takes much time, thereby the data transfer rate cannot be improved so much.